Orthodontic distalizing devices for correcting the relative position of the teeth of a dental arch are known. In such known devices of this kind, spring-loadable pusher means are generally arranged on the side opposite the lingual side of the dental arch. Moreover, the pusher means are interposed between the means for anchoring the framework to a tooth selected for that purpose and the means for fastening to the further tooth being distalized of the same branch of the dental arch. The reaction force exerted by the pusher on the tooth being distalized is not discharged completely onto the basal gingiva and underlying bony support of the arch, but can also act at least partially on the tooth selected for anchoring of the framework, thus resulting in the risk of causing displacement of the latter as well.
The pusher of the known distalizing apparatuses generally consists of a pusher pin which is fastened substantially tangentially to the tooth being distalized, and on which is mounted in coaxially sliding fashion a compression sleeve of a pusher spring. The spring is interposed between the head end of the pin, rigidly fastened to the means for fastening to the tooth being distalized, and the facing head end of the sliding sleeve. The latter is in turn joined to the anchoring means of the framework via wires or the like, with which it is held in the desired spring compression position. For this purpose the pusher pin must extend sufficiently beyond the anchoring tooth, in a direction opposite to the compression direction of the spring, as a result of which the pusher means have considerable dimensions and are thus retained non-rigidly or only in a direction opposite to the direction of spring compression on the anchoring tooth. The pusher pin therefore does not exert sufficiently precise directional guidance on the tooth to prevent the forces exerted by the pusher means from being expressed, even partially, as torques capable of causing tilting of the tooth from the correct vertical orientation and/or rotation thereof, and/or as components transverse to the longitudinal axis of the dental arch.
A number of relatively simple and low-cost designs which overcome all the above-identified drawbacks of conventional distalizing apparatuses are disclosed in U.S. Pat. No. 5,785,520, issued Jul. 28, 1998, which is hereby incorporated by reference in its entirety. According to one embodiment disclosed in the '520 patent, a distalizing apparatus 10 (illustrated in FIGS. 1-4 attached hereto) comprises a supporting framework 12 composed of an anatomical support element 14 (in the form of a Nance button) and a transverse structure 16 (in the form of a metal wire) embedded in Nance button 14. Framework 12 is anchored to a pair of anchoring teeth 18 and 20 by attaching the two opposed ends of transverse wire 16 to bands 22 and 24, respectively. Extending from Nance button 14 are two additional transverse structures 26 and 28 (also in the form of metal wires), both of which have ends joined by means of pusher elements 30 and 32 to bands 34 and 36, respectively, for fastening to teeth 38 and 40 being distalized.
In the illustrated embodiment, each pusher element 30, 32 generally comprises a pusher pin 42 and a narrow tube 44 that are telescopically engaged with one another (see FIG. 3), with an elastic element 46 (e.g., a compression spring as shown in FIGS. 1 and 2) captured therebetween. In addition, each pusher element includes a locking collar 48 that is slidably mounted on tube 44 so that compression spring 46 can be preloaded as desired by moving locking collar 48 towards or away from pusher pin 42 and locking it in position. Pusher elements 30 and 32 are assembled and installed in the dental arch with the proper position and orientation so that the forces generated thereby are exerted in the general direction of the longitudinal axis of the dental arch. During this installation process, the technician must take care when adjusting the position of locking collar 48 to ensure that pusher elements 30 and 32—including their associated springs and locking collars—remain in the fully assembled state to prevent the possibility of one or more elements being swallowed or aspirated.
As best seen in FIG. 2, the attachment points of pusher elements 30 and 32 to wires 26 and 28 are located as low as possible within the dental arch so that pusher elements 30 and 32 are within the basal zone of gingiva. Similarly, the attachment points of pusher elements 30 and 32 to bands 34 and 36, respectively, are also provided as low as possible above (or in) the cervical zone so as to be as close as possible to the centers of resistance of teeth 38 and 40. As recognized in the '520 patent, this arrangement largely suppresses those components of the distalizing force exerted by pusher elements 30 and 32 which otherwise would act to tilt teeth 38 and 40 from their correct vertical orientations.
To prevent pusher elements 30 and 32 from discharging any reactive forces on anchoring teeth 18 and 20, transverse anchoring wire 16 may be provided with a pair of respective force compensation means 50 and 52 (in the form of wire loops). Wire loops 50 and 52 are suitably elastically preloaded by the technician in the direction opposite to the reaction force components resulting from pusher elements 30 and 32 applying their desirable distalizing forces. To ensure that no reaction forces are exerted on the anchoring teeth 18 and 20, loops 50 and 52 must be carefully shaped to provide an offsetting bias force that is substantially the same magnitude but in the opposite direction as the anticipated reaction forces from pusher elements 30 and 32 acting against teeth 38 and 40 which are not absorbed by Nance button 14.
Another feature of distalizing apparatus 10 disclosed in the '520 patent is that pusher elements 30 and 32 may be converted into a rigid (or inactive) state to prevent further application of distalizing forces. This makes it possible to use distalizing apparatus 10 as an anchoring structure or molar retainer once distalizing has been successfully completed and when it is necessary to move the anterior teeth toward the distalized teeth to close any space that has been created.
According to the '520 patent, this conversion may be accomplished by providing a slit (or notch) 54 in the end of tube 44 (see FIG. 3) so that it can be readily clamped to pusher pin 42 to prevent any relative sliding movement therebetween (see FIG. 4). The '520 patent also mentions that this conversion process can be accomplished by applying a cold-setting or photo-activated resin to the junction of pin 42 and tube 44. Although the distalizing appliance 10 of the '520 patent when converted into a molar retainer by either of the foregoing methods can be reversed to restore pusher elements 30 and 32 to their active (or force-applying) states, the apparatus 10 must generally be removed from the patient's mouth in order to do so.
In view of the forgoing, it is an object of the invention to implement an orthodontic distalizing apparatus which, like the devices disclosed in the '520 patent, effectively eliminates all the above-noted drawbacks of conventional distalizing devices, while at the same time offering greater ease of installation, adjustment and conversion between the active and passive states.